Trace chemical detection of explosives, i.e., the art of detecting explosive materials from minute quantities of vapor and/or microscopic particles (hereinafter referred to as “particles”), can be an important aspect of many physical security and contraband detection systems. In many applications, especially applications involving the general public such as airport passenger screening, swipe collection of particles via direct physical contact with the person or object to be screened for explosives is either too physically invasive or time consuming, so it is advantageous to base the collection process on air flows. But the particle material that is collected in such air flows is usually far more dilute than the detector is capable of measuring, and the air flow is often too large to be directly accommodated by the detector. These disparities give rise to preconcentrators, devices which take a trace sample of a material from a large incoming air flow and concentrate the material into a smaller volume before it is introduced into a trace detector.
U.S. Pat. Nos. 5,854,431 and 6,345,545 disclose single stage and multi-staged preconcentrators, respectively, for use in collecting particles from an air stream that passes over a person or object under observation. While these preconcentrators concentrate particles in a high volume gas flow for detection in a low volume gas flow, they are best suited to low vapor pressure (LVP) explosive detection. Recently however, high vapor pressure (HVP) explosives have come into more common use such that both LVP and HVP explosive detection is needed. A means to collect and preconcentrate HVP explosives is therefore desirable.